6.5x284 chamber neck size advice

[WesternTX]

I'm getting my 6.5x284 rebarreled and my smith has a 6.5x284 296NK reamer. I use lapua brass, and loaded rounds with 143 Eldx bullets vary from in neck size .2935 to .295, but mostly around the .294 mark. I resize necks with a .292 bushing. The question is would I need to neck turn with the 296NK reamer, or should I go with the 6.5x284 Norma match chamber (297NK)?

 

[7.62 Gunner]

.002 isn't enough neck clearance, .004-.006 is where you want to be

 

[Mikecr]

IMO, there is no reason to have more clearance, as that's just more working of necks.
And your bushing choice sounds right.

If there is a matter to ping on, it's necks at 15thou thickness, for loaded OD of .294.
With seriously thick necks like that you can get a lot of springback/springback variance.
Personally, I would turn them to 13thou thickness and tighten the chamber neck accordingly, but you might just anneal frequently to manage this.

 

[Coyote Shadow Tracker]

Good evening
I designed a 6.5X284 with a .296 Neck, throated long for 142SMK and JGS made us the reamer. PTG also has a "Match" Reamer with a .297 neck.
If you want I can send you the prints to look over.
On another note we turn all the necks on cases just enough to make sure they are concentric.
Thanks
Len & Jill

 

[338 dude]

I'm getting my 6.5x284 rebarreled and my smith has a 6.5x284 296NK reamer. I use lapua brass, and loaded rounds with 143 Eldx bullets vary from in neck size .2935 to .295, but mostly around the .294 mark. I resize necks with a .292 bushing. The question is would I need to neck turn with the 296NK reamer, or should I go with the 6.5x284 Norma match chamber (297NK)?

Norma match reamer I've been using one for years!

 

[WesternTX]

IMO, there is no reason to have more clearance, as that's just more working of necks.
And your bushing choice sounds right.

If there is a matter to ping on, it's necks at 15thou thickness, for loaded OD of .294.
With seriously thick necks like that you can get a lot of springback/springback variance.
Personally, I would turn them to 13thou thickness and tighten the chamber neck accordingly, but you might just anneal frequently to manage this.

So no pressure concerns at ~.002 clearance?

Makes sense on potential springback variance concerns due to thickness and variance. I'm fairly green with reloading, would annealing impact loaded neck size? Or do you mean minimize springback variance?

 

[WesternTX]

Good evening
I designed a 6.5X284 with a .296 Neck, throated long for 142SMK and JGS made us the reamer. PTG also has a "Match" Reamer with a .297 neck.
If you want I can send you the prints to look over.
On another note we turn all the necks on cases just enough to make sure they are concentric.
Thanks
Len & Jill

Yes, please do.
What thickness do you target when turning?

 

[Coyote Shadow Tracker]

Yes, please do.
What thickness do you target when turning?

PM sent
.291 neck with a bullet in, and turned to 0.0135 wall thickness.

 

[Mikecr]

So no pressure concerns at ~.002 clearance?

No. Why do you think there would be?
Do you intend to crimp into bullets?

 

[WesternTX]

No. Why do you think there would be?
Do you intend to crimp into bullets?

No planning on crimping, was just thinking if 0.001-0.002 clearance would be enough to allow the case to open and pressure to escape without creating a pressure spike. Perhaps I'm thinking about it incorrectly.

 

[338 dude]

No planning on crimping, was just thinking if 0.001-0.002 clearance would be enough to allow the case to open and pressure to escape without creating a pressure spike. Perhaps I'm thinking about it incorrectly.

I like .003 to .004 clearance

 

[7.62 Gunner]

No planning on crimping, was just thinking if 0.001-0.002 clearance would be enough to allow the case to open and pressure to escape without creating a pressure spike. Perhaps I'm thinking about it incorrectly.

No you're thinking correctly, that's not enough clearance and you will have issues, especially with a dirty chamber.

 

[Mikecr]

No you're thinking correctly, that's not enough clearance and you will have issues, especially with a dirty chamber.

Dirty chambers, and neck-shoulder sooting comes from excess neck and chamber end clearances.
You got it back asswards.

'Pressure' is not relived with neck expansion, but with the released bullet moving forward.
It makes no difference with 1/2thou clearance or 10thou clearance, as the moment the neck expands a ~billionth of an inch the bullet is free.
The neck's role ends there.

Now, when you have a lot of excess clearance, gas works it's way around and between the neck and chamber, messing with good sealing (or preventing it).

 

[7.62 Gunner]

Dirty chambers, and neck-shoulder sooting comes from excess neck and chamber end clearances.
You got it back asswards.

'Pressure' is not relived with neck expansion, but with the released bullet moving forward.
It makes no difference with 1/2thou clearance or 10thou clearance, as the moment the neck expands a ~billionth of an inch the bullet is free.
The neck's role ends there.

Now, when you have a lot of excess clearance, gas works it's way around and between the neck and chamber, messing with good sealing (or preventing it).

Oh boy..